Outcome and Characteristics of Nonsecretory Multiple Myeloma Compared with Secretory Multiple Myeloma: A Retrospective Multicenter Study from China

Background Nonsecretory multiple myeloma (NSMM) is a rare type of multiple myeloma (MM). Few studies have described the clinical features and outcomes of NSMM in novel agents. Additionally, the prognostic characteristics have remained controversial in recent years. Purpose To investigate the clinical and prognostic features of NSMM and explore the prognostic value of involved free light chain (FLC) levels in NSMM patients in the Chinese population. Methods We retrospectively enrolled 176 newly diagnosed NSMM cases between January 2005 and December 2021 from 19 clinical centers in China. The control group was selected using a 1:4 propensity score matching technique of newly diagnosed secretory MM, with age, sex and diagnosis time as the matching variables. Results The median age of NSMM patients was 60 years, and 22.6% of patients were classified as ISS stage 3. The ORR of the NSMM patients was 87.4%, and the CR was 65.8%. Compared to the matched secretory MM patients, more NSMM patients achieved CR after first-line treatment (65.8% vs. 36%, p = 0.000). The ORR of first-line treatment was not significantly different between NSMM and secretory MM (89.45% vs. 84.7%, p = 0.196). The first-line PFS was 27.5 m and 23 m ( p = 0.063), and the median OS was 81 m and 70 months ( p = 0.401). However, for CR-achieved NSMM and CR-not-achieved NSMM patients, the median PFS was 37 m vs. 16 m ( p = 0.021), while the median OS showed no difference (107 m vs. 87 m, p = 0.290). In multivariate analysis, the significant factors for PFS were age ≥ 65 and ISS-3. ISS-3 was the only independent prognostic factor of OS. The iFLC ≥ 50 mg/L group had a high ORR of 97.3%, and the median PFS and OS were 48 m and NR, respectively. Compared to the matched secretory MM, the iFLC ≥ 50 mg/L group also showed more CR and longer OS (NR vs. 70 m, p = 0.006) and PFS (48 m vs. 23 m, p = 0.003). Conclusions Our results revealed that Chinese NSMM patients are younger and have a higher CR but not superior survival. The subgroup of NSMM patients with iFLC ≥ 50 mg/L had better outcomes than secretory MM.